randomSTR

public static String randomStr(int len){ 
            String str=""; 
            int num; 
            char ch; 
            for (int i=0;i<len;i++){ 
                num = (int)(Math.random()*26); 
                ch = (char) (num + (int)'a'); 
                str += ch; 
            } 
            return str; 
        }